Systems and methods for synchronous demodulation

Abstract

Systems and methods for synchronous demodulation using passive sampled analog filtering are disclosed. A system for synchronous demodulation includes an input channel for accepting an input signal, a first passive sampled analog filter for filtering the input signal, a mixer for mixing the filtered input signal and outputting a mixed signal, a second passive sampled analog filter for filtering the mixed signal, and an output channel for outputting the filtered mixed signal.

What is claimed is: 
     
       1. A system for synchronous demodulation using passive sampled analog filtering, comprising:
 an input channel for receiving an input signal; 
 a first passive sampled analog filter for sampling and filtering the input signal; 
 a mixer for mixing the filtered input signal from the first filter and outputting a mixed signal; 
 a second passive sampled analog filter for filtering the mixed signal; and 
 an output channel for outputting the filtered mixed signal. 
 
     
     
       2. The system of  claim 1 , wherein the first filter and the mixer are combined in a single passive circuit block. 
     
     
       3. The system of  claim 1 , further comprising a first active amplifier between the first filter and the mixer for amplifying the filtered signal. 
     
     
       4. The system of  claim 3 , further comprising a second active amplifier between the mixer and the second filter for amplifying the mixed signal. 
     
     
       5. The system of  claim 1 , wherein the first passive sampled analog filter is a programmable filter. 
     
     
       6. The system of  claim 1 , wherein the first passive sampled analog filter is one of a low-pass filter, a band-pass filter, a high-pass filter, and a filter with an arbitrary filter shape. 
     
     
       7. The system of  claim 1 , wherein the first passive analog filter is one of a FIR filter and an IIR filter. 
     
     
       8. The system of  claim 1 , wherein the second passive sampled analog filter is a low pass filter. 
     
     
       9. The system of  claim 1 , further comprising a clock generator for generating an excitation signal, and wherein the excitation signal is modified by a target element, and the modified excitation signal is the input signal. 
     
     
       10. The system of  claim 9 , wherein the target element is a body part and wherein the system measures bioimpedance of the body part. 
     
     
       11. The system of  claim 9 , wherein the clock generator generates a reference signal, and wherein the reference signal is mixed with the filtered input signal at the mixer. 
     
     
       12. The system of  claim 9 , wherein the target element is one of a sensor and a transformer. 
     
     
       13. A method for synchronous demodulation using passive sampled analog filtering, comprising:
 presenting an excitation signal to a target element; 
 receiving, at an input, a modified signal from the target element; 
 sampling and filtering, using a passive sampled analog filter, the modified signal to remove noise; 
 mixing the filtered signal with a reference signal from a clock generator; 
 filtering, using a second passive sampled analog filter, the mixed signal; and 
 outputting, from the second passive sampled analog filter, a signal representing characteristics of the target element. 
 
     
     
       14. The method of  claim 13 , wherein presenting the excitation signal includes presenting a current to the target element, and wherein receiving a modified signal includes receiving a voltage. 
     
     
       15. The method of  claim 13 , wherein presenting the excitation signal includes presenting a voltage to the target element, and wherein receiving a modified signal includes receiving a current. 
     
     
       16. The method of  claim 13 , wherein outputting the signal includes outputting an I-component of the signal and outputting a Q-component of the signal. 
     
     
       17. A synchronous demodulation system using passive sampled analog filtering, comprising:
 a clock generator for generating an excitation signal; 
 an input channel for receiving a modified excitation signal; 
 means for passively sampling, filtering and mixing the modified excitation signal to synchronously demodulate the modified excitation signal and generate a demodulated output signal. 
 
     
     
       18. The system of  claim 17 , wherein the means for passively filtering the modified excitation signal includes a passive sampled analog filter. 
     
     
       19. The system of  claim 18 , wherein the passive sampled analog filter is one of a low-pass filter, a band-pass filter, a high-pass filter, and a filter with an arbitrary filter shape. 
     
     
       20. The system of  claim 17 , wherein the means for mixing the modified excitation signal include a mixer, and wherein the mixer is one of a two-level mixer, a three-level mixer, and a mixer with greater than three levels.